Cool Stuff (Part I) 2003
The first of two articles by Alec McCarter, reprinted from the Finnerty Gardens newsletter.
Seated in our garden, warmed by the sun, I look at the great, almost bare rock that rises from the earth, deep-grooved and scratched by a long-forgotten glacier. Some 10 to 13,000 years ago, ice, perhaps a thousand meters thick, covered this very spot. The enormous weight pressed the land and rock below the surface of the sea. Thousands of years later as the ice melted and the weight was removed, the land emerged again. The rock has been smoothed, ice-scoured, and wind-weathered. Now, 100 meters above the sea, but still surrounded by marine clays, it bears a thin covering of lichens, moss, ferns, grasses and Sempervivums that someone planted in its crevices. A Garry oak is slowly enlarging a foothold in a crack. All that is left of its ordeal with the ice are the deep grooves and scratches, running North-South.
I try to imagine what that rock endured and what the future holds for it and us. At present there is great concern that so-called greenhouse gases, produced by Man's activities are changing the climate. There is much evidence that this is so. I will not argue otherwise, but will claim that it is now documented (see references below) that changes in the Earth's climate occurred and recurred long before man became the spoiler with his agriculture, burning of fossil fuels, the invention of the internal combustion engine and his knowledge of chemistry. Living things, including our ancestors, have been challenged by climate change many times in past eons.
Two recent studies of Antarctica are particularly revealing and convincing. The first, published in 1999 in the renowned science magazine Nature, was a study of the composition of gases encased in glacial ice at Vostok, the Russian base in the Antarctic. The study depended on the observation that newly formed ice traps air which is buried as bubbles in ice as it thickens, thus preserving a sample of the atmosphere. Cores of ice were drilled to a depth that made 400,000 years of the geological record available for analysis. This allowed estimates to be made of the dates at which events occurred; the temperatures that then prevailed; and the atmospheric concentrations of the greenhouse gases, carbon dioxide (CO2) and methane. The skeptical among us will question that such data could be valid, but they can be calibrated and are free from serious doubt. The analyses showed that in the period of 400,000 years before the present, there were four major, complete cycles of warming and cooling each lasting about 100,000 years. There were also shorter cycles of warmth and cold, less extreme, recurring at 40,000 year's intervals. Each peak and dip was accompanied by parallel variations in concentrations of CO2 and methane.
The theory to account for this, now supported by evidence, is that these changes occurred in concert with alterations in the amounts of solar energy reaching the Earth, and regularly cycling as a result of three phenomena, related because they depend on the gravitational influence of the other planets. One phenomenon, repeating every 100,000 years, relates to the oscillation in the Earth's orbit around the sun. The second phenomenon derives from changes in the inclination of the Earth's rotational axis every 40,000 years and the third concerns a wobble in the axis of rotation requiring 26,000 years for one cycle.
As it gets closer to the sun, the Earth warms. When the axis of rotation tilts so that the North pole points more directly at the sun, the Northern summer will be warmer, but the South will be colder because it points away from the sun. The reverse statements are also true. When these effects complement each other, as they do every 120,000 years or so, they produce excessive heating, but they can also combine to give excessive cooling and it is then that ice sheets advance. The Antarctic ice sheets, which began to form about 34 million years ago, expanded or contracted in response to changes in the Earth's movement in space, collectively called Milankovitch effects, after the Czech scientist who first developed the theory.
The authors of the Vostok study, estimated that these effects were roughly doubled by greenhouse gases, which they attributed to human occupation of the planet. Indeed, levels of methane have increased dramatically over the last two hundred years. No explanation was given for similar changes in composition of the atmosphere that took place before human beings were a factor.
The second study, with results published in Nature in October, 2001, involved scientists from seven nations and their analyses of cores drilled into the bottom of the Ross Sea of Antarctica. These rock cores were made up of sediments going back to nearly 24 million years ago. Within a portion of the core representing about 15 million years of Antarctic history were 46 complete cycles, each containing layers of similar sedimentary composition, interpreted to be the result of 46 cycles of glacial advances and retreats. Within a 400,000 year segment of that core, with valid markers of dates, warming and cooling recurred with periods of 100,000 and 40,000 years. These findings are in remarkable agreement with those from the study of the gases that had been trapped in ice of much more recent history. Some of the raw data for this study are available on the Internet. (See "Further Reading" below.)
In the Northern hemisphere, the great Ice Age of North America and Eurasia began about 1.8 million years ago. It too, like the Antarctic ice sheet, was subject to advances and retreats documented from geological features, presumably in rhythm with the Milankovitch effects. The last major advance began about 130,000 years ago and lasted until about 20,000 years before the present. A relatively rapidly rising temperature, melted all but the ice cap over Greenland, remnants in Alaska, the Arctic, and the mountains. Now, temperatures and values for atmospheric C02 and methane are about as high as they have been many times before, preceding abrupt cooling. Predictions have been made by climatologists of still higher values to be reached with horrendous effects on climate, including droughts, terrible storms, melting of ice at the Poles and higher sea levels leading to drowned cities and other catastrophes.
The evidence is that comparable events have happened before. They appear to be normal consequences of the Earth's surface being closer to or further from the sun, according to a schedule as old as the Earth. These events take place in time on a vast scale that challenges our imaginations and reasoning powers.
1. "Water and Atmosphere : Antarctic Ice: The World's Air Museum," NIWA Vol. 9, March 2001, http://www. niwa.co nz/ pubs/wa/09-1/ice.htm.
2."Climate Variability and Change: Past Climate Changes Over New Zealand," HYPERLINK http://www.niwa.co.nz/rc/atmos/clivar/pastclimate.
3. "Antarctic Seafloor Core Suggests Earth's Orbital Oscillations May Be The Key To What Controlled Ice Ages," HYPERLINK http://www.sciencedaily.com/releases/2001/10/011018071615.htm .
Further reading on the Internet:
1."Antarctic Cores Reveal Ice History," BBC News October 18, 2001, news.bbc.co.uk/hi/english/sci/tech/ newsid. Includes picture of the drilling rig on the ice-shelf.
2. John Wainwright, "Long Term Climate Change,"HYPERLINK http://www.kce.al.uk/kis/schools/hums/geog/cw/fs/longtermclimatechange.pdf. An excellent article with diagrams.
3. Helen Neil, ."Back to the Future: Productivity Upheaval in a Warming Ocean," http://www. niwa. co.nz/ pubs/ wa/09-4/productivity.